1. Field of the Invention
The present invention relates to writing magnetic heads, and particularly to a writing magnetic head having an increased saturation magnetic flux density in the vicinity of a gap layer and satisfying the requirements for high recording density.
2. Description of the Related Art
FIG. 18 is a front view of a known writing magnetic head. The magnetic head is a so-called inductive head Hw, which is disposed on a reading magnetic head Hr using, for example, a magnetoresistive effect.
The reading magnetic head Hr comprises a magnetic field-reading element 1. A lower shield layer 3 and an upper shield layer 4 are disposed on both surfaces of the magnetic field-reading element 1 each having a gap layer 2 between the respective shield layers 3 and 4 and the element 1. The magnetic field-reading element 1 is a magnetoresistive sensor M comprising a GMR element using a giant magnetoresistive effect, such as a spin-valve film, or an AMR element using an anisotropic magnetoresistive effect.
The length of the magnetic field-reading element 1 in the track width direction defines the track width Tr of the reading magnetic head Hr. The distance between the upper shield layer 4 and the lower shield layer 3 is H2.
The gap layer 2 is formed of an insulating material such as Al2O3 or SiO2. The lower shield layer 3 and the upper shield layer 4 are formed of a soft magnetic material having a high magnetic permeability, such as a NiFe alloy (permalloy).
The inductive head Hw comprises an insulating layer 5 on the upper shield layer 4 which also serves as a lower core layer 4 as well as a shield layer.
The insulating layer 5 has a slit 5a having a predetermined length which is formed from the face (ABS face) opposing a recording medium in the height direction (the Y direction in the drawing).
The slit 5a is provided with a lower magnetic pole layer 6, a gap layer 7, and an upper magnetic pole layer 8 therein by plating. The lower magnetic pole layer 6 is magnetically coupled with the lower core layer 4. The lower magnetic pole layer 6, the gap layer 7, and the upper magnetic pole layer 8 form a magnetic pole P defining the track width Tw. The track width Tw is 1.0 μm or less and is preferably 0.8 μm or less.
The lower magnetic pole layer 6 and the upper magnetic pole layer 8 are formed of a magnetic material such as a NiFe alloy, and the gap layer 7 is formed of a nonmagnetic metal such as a NiP alloy.
An upper core layer 9 is formed of a magnetic material such as a NiFe alloy on the upper magnetic pole layer 8 by plating. The upper core layer 9 has a width larger than the track width Tw.
A coil layer (not shown) is spirally patterned on the insulating layer 5 extending in the height direction.
A writing current flowing in the coil layer induces a writing magnetic field to the lower core layer 4 and the upper core layer 9, and thus causes a leakage field between the lower magnetic pole layer 6 and the upper magnetic pole layer 8, which oppose each other separated by the gap layer 7. The leakage field serves to write magnetic signals on recording media such as hard disks.
The known magnetic head as shown in FIG. 18 has the lower magnetic pole layer 6 and the upper magnetic pole layer 8, which oppose each other separated by the gap layer 7, in the slit 5a. Thus, the leakage field generated between the upper magnetic pole layer 8 and the lower magnetic pole layer 6 can be limited to the track width Tw of 0.1 μm or less.
The magnetic pole P, which comprises the lower magnetic pole layer 6, the gap layer 7, and the upper magnetic pole layer 8, is formed by electroplating in a slit formed in a resist layer or the like having a width equivalent to or slightly larger than that of the slit 5a. 
In order to increase recording density, the saturation magnetic flux density must be large in the vicinity of the gap layer 7. Accordingly, the lower magnetic pole layer 6 and the upper magnetic pole layer 8 are formed of a magnetic material having a Fe content of 60% or more.
However, such a magnetic material having a high Fe content causes dispersion of the composition thereof in the lower magnetic pole layer 6 and the upper magnetic pole layer 8 when the magnetic pole P has a track width of 1.0 μm or less.
FIG. 19 shows changes in the Fe content of the upper magnetic pole layer 8 formed of a NiFe alloy.
FIG. 19 shows the relationship between the distance from the under surface 8a of the upper magnetic pole layer 8 in the Z direction in the drawing and the Fe content of the interior of the upper magnetic pole layer 8.
FIG. 19 suggests that when the upper magnetic pole layer 8 is up to 300 nm away from the under surface 8a in the Z direction, the Fe content of the upper magnetic pole layer 8 changes in the range of 58 to 74 mass %.
The change in the composition of the upper magnetic pole layer 8 makes the saturation magnetic flux density unstable in the vicinity of the gap layer 7. As a result, it is difficult to improve the writing performance of the magnetic head while recording density is being increased.